1. Field of the Disclosure
An embodiment of the present disclosure relates to a dual comb electrode structure with spacing for increasing a driving angle of a microscanner and the microscanner adopting the same, and more particularly to a dual comb electrode structure with spacing for increasing a driving angle of a micro mirror provided by MEMS (Micro-Electro-Mechanical system) structure and a microscanner adopting the same.
2. Description of the Related Art
As a microscanner for deflecting laser beam in a projection TV or the like, a micro actuator with MEMS structure using electrostatic effects by means of comb-type electrode structure is used. FIG. 1 is a perspective view exemplarily showing such a conventional microscanner. As shown in FIG. 1, the conventional microscanner includes, for example, a mirror unit 1 suspended above a substrate 5 made of silicon-on-insulator (SOI) wafer or the like, a support 6 for supporting both ends of the mirror unit 1, a torsion spring 2 connected between the mirror unit 1 and the support 6 to support seesaw movement of the mirror unit 1, a plurality of movable comb electrodes 3 vertically formed in both sides of the mirror unit 1, and a plurality of static comb electrodes 4 vertically formed on the substrate 5 so as to be alternated with the movable comb electrodes 3.
FIG. 2A is a sectional view for illustrating operation of the conventional microscanner configured as mentioned above. In the microscanner shown in FIG. 1, a predetermined voltage is applied to the movable comb electrodes 3 at both sides of the mirror unit 1, and positive and negative voltages are respectively applied to the static comb electrodes corresponding to the movable comb electrodes 3 at both sides of the mirror unit 1. For example, V voltage is applied to a left static comb electrode 4a, −V voltage is applied to a right static comb electrode 4b, and V1 voltage is applied to both left and right movable comb electrodes 3a and 3b. And then, a voltage difference between the left movable comb electrode 3b and the left static comb electrode 4a (V−V1) is different from a voltage difference between the right movable comb electrode 3b and the right static comb electrode 4b (V+V1), so the mirror unit 1 becomes inclined to one side by an electrostatic force as shown in FIG. 2A. The mirror unit 1 is restored by means of its own restoring force using the modulus of elasticity of the torsion spring 2. Thus, the mirror unit 1 may be periodically moved at predetermined driving angle and driving speed (or, a driving frequency) by suitably adjusting the voltage V1 applied to the movable comb electrodes 3.
Meanwhile, in order to realize an image on a screen by a laser image projection device such as a projection TV, a microscanner should scan laser beams at a very high speed. Since the driving frequency is in inverse proportion to weight, the mirror unit 1 is generally reduced to a size of about 1 mm and a thickness of about 70 μm to decrease the weight. Since the mirror unit 1 has a reduced size as above, a diameter of laser beam reflected by the mirror unit 1 is also reduced. However, if the beam diameter of the laser beam is reduced, the laser beam may be diffused at edges of the screen. This phenomenon is apt to cause deterioration of resolution of the laser image projection device.
Thus, in order to enhance resolution of the laser image projection device, it is required to increase the size of the mirror unit 1 so that a laser beam with larger beam diameter may be reflected or to increase a driving angle of the mirror unit 1. Accordingly, as shown in FIG. 2B, upper static comb electrodes 7a and 7b are added in the upper portion of the mirror unit 1 so as to double a driving force, which also doubles the driving angle.
However, if the size of the mirror unit 1 is increased, its weight is also increased to deteriorate a driving speed of the microscanner. In addition, there is also a limit in increasing a driving angle of the mirror unit 1. It is because, if the movable comb electrodes 3 at both sides of the mirror unit 1 are completely put into the static comb electrodes 4, driving force is not generated any more and the mirror unit 1 is thus not rotated any more. In this case, in order to increase a driving angle, it is required to increase the heights of the movable comb electrodes 3 and the static comb electrodes 4 so that an angle at which both kinds of electrodes are completely overlapped becomes larger. Thus, in order to increase a driving angle, the thickness of the mirror unit 1 should be increased, which also causes increase of weight of the mirror unit 1.